A typical wireless communication apparatus, such as a mobile terminal, is required to scan a range of radio frequencies in order to identify available communication systems and radio frequency (RF) carrier signals. In order to decode information transmitted by a communication system, the mobile terminal is required to synchronize to the system, for which purpose synchronization information is transmitted by base stations of the communication system.
For example, in a communications system operating in accordance with the GSM standard, a base station in each cell transmits, on a broadcast control channel (BCCH), a frequency correction channel (FCCH) and a synchronization channel (SCH). The FCCH enables a mobile terminal to synchronize its local oscillator to the base station and then to receive the synchronization channel (SCH), which provides further synchronization information. The FCCH consists solely of a tone burst at 67.7 kHz relative to a carrier center frequency. On those carrier signals conveying the FCCH, the FCCH is transmitted once every 10 frames, corresponding to a rate of once every 46.15 ms, and the tone burst has a duration of 576.92 μs.
After initial power-on, a GSM mobile terminal typically tunes sequentially to available RF carrier signals that could potentially convey the broadcast channel of suitable cells, and measures the received signal strength of each of these channels. Each time that a carrier signal having a sufficient received signal strength is detected, the mobile terminal attempts to detect the FCCH and synchronize the frequency of its local oscillator to the carrier signal, and then attempts to detect the SCH and synchronize to the GSM frames and time slots, followed by decoding broadcast system information to check the suitability of the cell.
A multi-mode mobile terminal, capable of operating in accordance with more than one radio access technology (RAT), is potentially required to measure the received signal strength and perform cell selection for each carrier signal of each RAT. For example, the mobile terminal may evaluate carriers for each RAT in an order of preference until a suitable cell is identified, such as a fourth generation (4G) technology first, followed by a third generation (3G) technology, and finally a second generation (2G) technology. Such a process can result in an undesirably long delay before a cell is selected.
The Background section of this document is provided to place embodiments of the present invention in technological and operational context, to assist those of skill in the art in understanding their scope and utility. Unless explicitly identified as such, no statement herein is admitted to be prior art merely by its inclusion in the Background section.